Without any exception, all of the existing mass flowmeters known as the Coriolis force flowmeters employ a pair of vibrating conduits, which are vibrated relative to one another in a flexural mode by an electromagnetic vibrator disposed at the midsection of the combination of the pair of conduits intermediate the two fixed extremities thereof (see the embodiments shown in FIGS. 9 through 13), wherein the electromagnetic vibrator produces a primary flexural vibration of the conduits in a symmetric mode about the midsections of the conduits. The inertia force of the fluid moving through the conduits produces a secondary flexural vibration of an antisymmetric mode about the midsection of the conduits as a result of dynamic reaction to the primary flexural vibration. The level of the antisymmetric secondary flexural vibration measured relative to the level of the symmetric primary flexural vibration is proportional to the amount of mass flow rate of fluid moving through the conduit. One of the most popular methods of measuring the relative level of the antisymmetric secondary flexural vibration as a measure of the mass flow rate of the fluid is to measure the phase angle difference between two vibratory motions respectively detected by a pair of motion detectors measuring the total flexural vibratory motions (sum of the symmetric primary and antisymmetric secondary vibrations) at two sections of the combinations of the conduits disposed symmetrically about the midsections of the combination of the pair of conduits.
Hyok S. Lew has invented a number of new mass flowmeters known as the convective inertia force flowmeters (see the embodiments shown in FIGS. 1 through 6), which employs a single conduit wherein the two opposite halves of the conduit are vibrated relative to one another in a flexural mode, which are in contrast to the pair of conduits employed in the existing Coriolis force flowmeter wherein both halves of each of the pair of conduits is vibrated in unison. The primary flexural vibration of the single conduit employed in the inventions by Lew is antisymmetric about the midsection thereof, and the secondary flexural vibration thereof is symmetric about the midsection of the single conduit, which contrast the symmetric primary and antisymmetric secondary flexural vibration of the pair of conduits employed in the existing Coriolis force flowmeter (compare FIGS. 7 and 8). Because of the above-mentioned difference in the mode of flexural vibration of the conduit, a new method of measuring the relative level of the symmetric secondary flexural vibration as a measure of the mass flow rate is in order, which method is specifically designed for the convective inertia force flowmeters invented by Lew and has a certain advantage over the conventional method involving the measurement of the phase angle difference.